Why use LuaJIT over plain Lua here? I can't imagine that you need the extra speed in a text editor. The ffi is available for normal lua too: https://github.com/facebook/luaffifb/
So here's something to pop up a message box on Windows:
local ffi = require("ffi")
ffi.cdef[[
int MessageBoxA(void *w, const char *txt, const char *cap, int type);
]]
ffi.C.MessageBoxA(nil, "Hello world!", "Test", 0)
Compare this with the effort required to bind that function using the classic Lua/C API: create an extra C file, add a C function that retrieves and checks the argument types passed from Lua and calls the actual C function, add a list of module functions and their names, add a luaopen_* function and register all module functions, compile and link it into a shared library (DLL), move it to the proper path, add Lua code that loads the module aaaand ... finally call the binding function. Phew!
On the down side, TCC doesn't support all the architectures I use, so I mostly use it for proof-of-concept and throw away code.
One thing I keep thinking is to possibly use TCC (or parts of it) to parse C header files directly, so it would be easier to use an FFI in Lua.
[1] https://github.com/spc476/lua-conmanorg/blob/master/src/tcc....
[2] https://github.com/spc476/lua-conmanorg/blob/master/lua/cc.l...
[3] https://github.com/spc476/LPeg-Parsers/blob/json-1.0.0/json....
I think the main argument against Lua + luaffifb is that it might require an external dependency: luarocks. Whereas if someone were to theoretically provide Lua integration with emacs, it might be a good idea to offer the ffi library as a baseline feature.
This is a weak argument, because it should be possible to embed luaffifb plus Lua inside of a linked library, with no need to depend on luarocks.
It's probably best to explore both options.
My mouth was hanging open when I discovered that you could literally a verbatim header with packed structs and use it and it would work. Then I looked at the source to find out what they were using as a compiler frontend; it's all hand written. Incredible.